The Manchester City defender has already been suspended indefinitely. City and the FA confirmed last night that an 'A' sample had proved positive. Toure can opt to have his 'B' sample, taken in the same drugs test, analysed in a bid to prove his innocence.

It is the first positive test in English football since an unnamed player was banned after testing positive for cocaine in January last year. City were informed of the results of the test late on Wednesday afternoon and duly withdrew the player from their squad for the FA Cup fifth-round tie with Aston Villa. The failed test automatically triggered the suspension.

How long Toure is banned for, should he be found guilty, will depend on the substance involved, the explanation for how it was in his body and any mitigating circumstances.

According to the code of the World Anti-Doping Agency (WADA), "specified substances" are those that are "more susceptible to a credible, non-doping explanation." Those substances on the list can be used to enhance performance but can also be found in legitimate therapies, such as cold cures. Most common recreational drugs would not fall into the same category.

Even if Toure can prove that he only ingested a prohibited substance unknowingly, his punishment, according to Wada, could still be as draconian as a two-year ban. It is unlikely that he will play again this season as he fights his case.

The most recent precedent is Ireland's former Sheffield United goalkeeper Paddy Kenny, now with QPR, who was banned for nine months in September 2009 after testing positive for ephedrine, a prohibited substance found in cold remedies. The FA accepted that he had not deliberately sought to enhance performance when taking an over-the-counter remedy without consulting United's medical team.